Optical modules for processing light signals contain different optical components, such as purely optical or opto-electric components, for example opto-electric converters (generally laser diodes or photodiodes), amplifiers or modulators. Such components are coupled with optical fibres, normally glass fibres, but optionally also plastic fibres. Among other things, the power output of such optical modules is dependent upon the quality of this coupling.
As the diameter of the modal field at the input and/or output (in the following abbreviated to input/output) of such components is distinctly smaller than that of the modal field in the core of the optical fibre, different techniques have been developed to optimise the coupling. It has long been prior art to provide the input/output of the optical component with a waveguide whose end facing towards the optical fibre is tapered, for example in the form of a frustum, or is widened. Optionally, the waveguide and the core of the optical fibre can lie on the same axis. As a result of the oblique surfaces at the taper (for example the frustum) the modal field is enlarged by the light radiating therefrom, so that ideally a diameter is achieved which is equal to that of the modal field at the input of the optical fibre. Accordingly, modal field converters (“spot-size converter” or “taper”) are referred to. Such tapered/widened ends are generally structured directly in the same layer (for example in a semiconductor layer made of doped InP) in which the optical component was formed, either vertically or horizontally or even in both directions of the plane (see e.g. H. Oohashi et al. ECOC97, No. 448, p. 351-354, 1997).
It is also prior art (see e.g. DE 34 15 576) to use miniaturised lenses as modal field converters. This enables the efficiency of this coupling to be considerably increased. However the use of miniaturised lenses has the disadvantage of the extremely poor adjustment. The outlay required to achieve a satisfactory coupling with the high tolerance requirements is correspondingly high.
A combination of taper-like modal field converter and miniaturised lenses partially facilitates a good coupling. However the adjustment problems associated with the miniaturised lenses remain. Consequently the costs of optical modules designed in this way cannot be sufficiently reduced. This remains a considerable obstacle to their further development.